2.any of various proteins, as pepsin, originating from living cells and capable of producing certain chemical changes in organic substances by catalytic action, as in digestion. Supplement
Enzyme is usually a protein molecule with a characteristic sequence of amino acids that fold to produce a specific three-dimensional structure, which gives the molecule unique properties. Other molecule with catalytic activity is ribozyme, an enzyme made of RNA rather than protein.
Enzymes are usually classified and named according to the reaction they catalyze. The International Union of Biochemistry and Molecular Biology have developed a nomenclature for enzymes, the EC numbers. They are as follows: